This invention relates generally to web feeding devices and more particularly to the feeding of a web from an arborless roll over a dancer bar.
The supply of paper for an output printer is frequently in the form of a continuous web either prefolded in the fan-fold form or in a continuous roll. In the latter form, the roll may be supported on a spindle within the printer for incremental feeding or left unsupported in an arborless roll restrained typically in a V-shaped trough or cradle. The paper is then led from the roll over a resiliently supported dancer bar to web advancement means and the print station. Arborless rolls are frequently preferred because it is simpler for a machine operator to place the roll in a trough than to place it on a spindle. In addition, there are fewer accessory pieces of equipment such as spindles or centering hubs to be assembled or stored. A common trough can frequently be used to support webs of different widths and rolls of different diameters. A further advantage of arborless rolls is the inherent braking action resulting from roll friction against the trough or roll support surface. Spindle supported rolls frequently require a braking device to control the unreeling of the web when pulled suddenly and incrementally for controlled line feeding.
The arborless roll, however, has a significant disadvantage if there is a loose layer or coil on the outside of the supply roll in the trough. This looseness can occur at the time that the paper is loaded or be caused by the pinch point where the roll contacts the trough surface which tends to introduce slack in one or more of the outer layers of paper. The loose layers do not normally diminish in size as the paper web is fed through the printer. These layers can move endwise with respect to the roll causing paper tracking problems in the printer or damaging the paper by folding over the end of the roll.
The web is frequently drawn over a resiliently supported dancer bar to absorb some of the sudden pull on the web when advanced incrementally in the printer. There is, however, little control over the feeding since the increment of advancement is a constant and the weight and friction of the roll is constantly changing due to consumption.